You don't need to know much for the arduino part. Arduino is very easy to program for and the device won't do very much. Anybody who knows C should be able to get it going. I think the harder part is patching the bitcoin client to do the transaction import and export, and getting that accepted and integrated into the GUI. I did see some guys on the forum here who said they have Arduino experience. Some google searches would probably find them all.
If someone can get a hardware prototype running, I could just look through the Google bitcoinj source for the implementation details of how they store a signed transaction and push it to the network. From there, it's just adapting their code to make a mini script. Once a proof of concept works and can add transactions to the network, then it'll be easier to propose an addition to the bitcoin client.
Thanks for the search idea, it should've occurred to me
